An electromagnetic clutch mechanism, which enables or disables conduction of a rotational drive force from a driving-side rotatable body to a driven-side rotatable body through energization or deenergization of an electromagnetic coil, is known. In this type of clutch mechanism, when the electromagnetic coil is energized, the driving-side rotatable body and the driven-side rotatable body are coupled with each other to conduct the rotational drive force from the driving-side rotatable body to the driven-side rotatable body. When the electromagnetic coil is deenergized, the driving-side rotatable body and the driven-side rotatable body are decoupled from each other to disable the conduction of the rotational drive force from the driving-side rotatable body to the driven-side rotatable body.
However, in this type of electromagnetic clutch mechanism, at the time of coupling between the driving-side rotatable body and the driven-side rotatable body to conduct the rotational drive force, the electromagnetic coil must be always energized throughout the time period of coupling between the driving-side rotatable body and the driven-side rotatable body. Thereby, the electric power consumption (the energy consumption) is disadvantageously increased.
In view of the above disadvantage, the Patent Literature 1 proposes a self-holding type clutch mechanism, in which a permanent magnet is used to eliminate a need for energizing the electromagnetic coil at the time other than the time of coupling between the driving-side rotatable body and the driven-side rotatable body and the time of decoupling between the driving-side rotatable body and the driven-side rotatable body to reduce the electric power consumption.
This self-holding type clutch mechanism includes an electromagnetic coil, a permanent magnet, and a movable member. The electromagnetic coil includes first and second coil portions, which are respectively configured into a ring form centered at a rotational axis of the compressor and are arranged one after another in the axial direction of the rotational axis. The permanent magnet is configured into a hollow cylindrical form and is held between the first coil portion and the second coil portion. The movable member is configured into a ring form centered at the rotational axis and is movable in the axial direction.
In the clutch mechanism, the movable member is placed on an outer side of the first and second coil portions and the permanent magnet in a radial direction of the rotational axis. The permanent magnet generates an attracting magnetic circuit and a non-attracting magnetic circuit. The attracting magnetic circuit generates a magnetic attractive force that couples between the driving-side rotatable body and the driven-side rotatable body. The non-attracting magnetic circuit does not generate the magnetic attractive force. A resilient member is provided to exert a resilient force, which decouples between the driving-side rotatable body and the driven-side rotatable body.
For example, an electric current is conducted through the first and second coils in a first direction. In this way, a magnetic force, which is generated from the attracting magnetic circuit by the electromagnetic force generated from the first coil portion, becomes small, and a magnetic force, which is generated from the non-attracting magnetic circuit by the electromagnetic force generated from the second coil portion, becomes large.
In response to this, the magnetic force, which is generated from the non-attracting magnetic circuit, becomes larger than the magnetic force, which is generated from the attracting magnetic circuit. At this time, the movable member is moved toward one side in the axial direction by the magnetic force generated from the non-attracting magnetic circuit. Thereby, the resilient force of the resilient member becomes larger than the magnetic attractive force generated from the attracting magnetic circuit, so that the driving-side rotatable body and the driven-side rotatable body are decoupled from each other by the resilient force of the resilient member. That is, the clutch mechanism is placed into the OFF state.
In contrast, the electric current is conducted through the first and second coil portions in a second direction that is different from the first direction. In this way, a magnetic force, which is generated from the attracting magnetic circuit by the electromagnetic force generated from the first coil portion, becomes large, and a magnetic force, which is generated from the non-attracting magnetic circuit by the electromagnetic force generated from the second coil portion, becomes small.
In response to this, the magnetic force, which is generated from the attracting magnetic circuit, becomes larger than the magnetic force, which is generated from the non-attracting magnetic circuit. At this time, the movable member is moved toward the other side in the axial direction by the magnetic force generated from the attracting magnetic circuit. In this way, the magnetic force, which is generated from the attracting magnetic circuit, becomes larger than the resilient force of the resilient member, so that the driving-side rotatable body and the driven-side rotatable body are coupled with each other. That is, the clutch mechanism is placed into the ON state.
As discussed above, the movable member is moved to the one axial end side or the other axial end side by conducting the electric current through the first and second coil portions in the first direction or the second direction to turn on or off the clutch mechanism.
In the self-holding type clutch mechanism described above, the driven-side rotatable body is attracted and is coupled to the driving-side rotatable body at the time of changing from the OFF state to the ON state.
The driven-side rotatable body is magnetically attracted by the electromagnetic force of the electromagnetic coil and the magnetic force of the permanent magnet. Here, the driven-side rotatable body is magnetically attracted by the electromagnetic force of the electromagnetic coil and the magnetic force of the permanent magnet. Therefore, when the electromagnetic coil is energized upon the holding of the position of the movable member with the permanent magnet after completion of the coupling of the driven-side rotatable body, the excess electric power consumption and the excess heat generation of the electromagnetic coil may disadvantageously occur.
The excess heat generation of the electromagnetic coil may result in the temperature increase of the permanent magnet, which is placed adjacent to the electromagnetic coil, to cause a deterioration in the performance of the permanent magnetic and thereby to possibly result in a deterioration of the torque transmission performance of the clutch.
Furthermore, when the energization of the electromagnetic coil is terminated before the completion of the coupling of the driven-side rotatable body and the movement of the movable member, an erroneous operational state, such as an unachievable ON state of the clutch mechanism, may occur, or slipping may occur at coupling surfaces between the driven-side rotatable body and the driving-side rotatable body due to shortage of the magnetic attractive force to cause a deterioration in an NV (Noise and Vibration) performance.
Also, when the termination of the energization of the electromagnetic coil before the completion of the coupling of the driven-side rotatable body and the movement of the movable member is repeated, the coupling surfaces may be abnormally worn to cause an increase in a size of a gap between the driven-side rotatable body and the driving-side rotatable body at the clutch OFF time to cause a deterioration in the clutch operability and thereby to result in the unachievable ON state of the clutch.
At the time of changing the operational state of the clutch from the ON state to the OFF state, when the electromagnetic coil is energized upon the holding of the position of the movable member with the permanent magnet after completion of the decoupling of the driven-side rotatable body from the driving-side rotatable body and the movement of the movable body, the excessive electric power consumption and the excessive heat generation of the electromagnetic coil occur.
In view of the above matter, it is understood that an appropriate determination must be made for termination of the energization of the electromagnetic coil in order to reliably operate the clutch mechanism and to implement the clutch performance throughout the required product lifetime.